Device for detecting vapor leakages

ABSTRACT

The device is used for detecting leakages of steam contained in hollow bodies, particularly in pipes (26). It is intended for tending high temperature steam conduits. The hollow body is surrounded by a thermal insulation (24) containing a measuring chamber (28). A temperature sensor (32) and a steam detector (9, 18) are disposed within that measuring chamber. Signalling apparatus announces the simultaneous presence of steam and temperature drop. When the pressurized steam contained in the hollow body or in the conduit happens to leak, it expands thereby producing a temperature drop. The sensing of both effects, i.e. the temperature drop and the presence of vapor avoids erroneous warnings.

The present invention is with respect to a device for detecting steamleaking from hollow bodies, more specially pipes.

The invention is more specially important for keeping a watch onsuperheated steam ducts, more specially in nuclear power plant. In theprior art, there have been three ways of doing this so far:

(1) Inspection by those running the plant, something which is notpossible all the time and without danger, in nuclear plant, to thoseinspecting.

(2) Measuring the pressure. It is then not possible for small leaks tobe detected and changes in pressure caused by other effects than leaksgive a false alarm.

(3) Measuring radio-activity if the steam in the pipes is radio-active.However, the radio activity of the steam is not constant so that falsealarms are produced. Furthermore, this method is not very sensitive.

The present invention is based on the fact that the development of thestart of a sub-crititcal steam pipe crack into a full burst takes a longtime, for example 60 minutes, long enough for shutting down the steampipe in danger. However, it is necessary to have some way of quicklydetecting the start of a cracking process, which will be marked by theleaking of steam out of the pipe.

The purpose of the invention is to make this possible. Furthermore,false alarms are to be stopped as far as possible.

This purpose is effected by the invention as made clear by the followingdescription and claims.

In the invention two different physical effects are measured, namely onthe one hand a leaking of steam out into the measuring space and on theother hand a temperature drop in the same. On steam under gage pressurein the pipe or other hollow body making its way out through a leak,there will be expansion and a fall in temperature of the steam, thedegree of such a temperature drop giving a certain and safe measurement.By measuring the two different effects, it will generally not bepossible for false alarms to be produced, the device only producing anoutput signal, such as an alarm signal, on the two effects taking placeat the same time.

The useful effects of the invention are: full-time monitoring of thesystem. Monitoring may be undertaken from a great distance away so thatthere is no danger to workers. Furthermore, low rates of leaking may besafely detected. Because of the high sensitivity, sub-critical leaks maybe detected so early on that there is enough time for shutting down thepart of the plant in question, that is to say it is not necessary forthe plant to be very quickly shut down as an emergency in a power plantfor example. The device is low in price and upkeep is simple.

Using the further development of the invention, the position of a leakmay be made out without any trouble so that, once the fact that a leakis present has become clear, the discovery of its position without muchtime being necessary for looking for it will be possible.

Using the still further development of the invention, a number ofmeasuring points may be spaced out along each length so that near eachpoint, at which a leak is likely, there will be at least one measuringpoint. Having a number of like measuring feelers on each length makesoperation safer. Furthermore, a reading is quickly produced.

The system is very simple and, for this reason, low in price.

A further development gives a high reading sensitivity and makes itpossible for the position of damage to be made out.

Further with respect to different feelers for temperature and steam, allgive a sensitive and quick reading.

An account will now be given of embodiments of the invention using thefigures.

FIG. 1 is a perspective view and part axial section of a coaxial form ofsteam detector.

FIG. 2 is a view on the same lines of a steam detector in the form of awith parallel electrodes and a steam inlet pipe next thereto

FIG. 3 is a view of a further form of a steam detector as in FIG. 2.

FIG. 4 is a perspective view of a piece of steam piping with parts oftwo insulating cases, a temperature feeler and two steam detectors.

FIG. 5 is a view of other steam detectors, the general system being inother respects as in FIG. 4.

FIG. 6 is an exemplary warning instruments.

In the embodiments of FIGS. 1 and 2 there is, in each case, a housing 2having a pipe 4, the two being made for example of steel. In FIG. 1 ametal rod 6 will be seen running downwards into the middle of thehousing 2, the rod, however, ending some distance short of the end ofpipe 4. The space between the rod 6 and the pipe 4 and thereover isfilled up with insulating material 8, in the present case ceramicmaterial or sintered grains of glass. The selection of the insulatingmaterial and the materials of the pipe 4 and the rod 6 is such that theyhave roughly the same coefficients of thermal expansion so that thesteam detector, generally numbered 9, is not damaged by thermal loads.Rod 6 and housing 2 are used as two electrodes and have leads, 10 in theone and 11 in the other case.

In the device of FIG. 2, pipe 4 is kept empty, the steam detector 13 inthe limited sense of the word being fixed in housing 2 so that its topface is uncovered and facing into the pipe. Inside the insulatingmaterial 15 there are two electrodes 27, parallel to each other andhaving insulating material all round them (so that they are only to beseen in the section). Again, they have leads 10 and 11. FIG. 3 is a viewof a further form of a contact steam detector 18, two electrodes 20, forexample in the form of round plates, cased in insulating material 15 andhaving leads 22 running from the electrodes to the outside.

FIGS. 4 and 5 are, in each case, a view of a length of steam pipe 26having two insulating cases 24 placed round it for heat insulation. Thefront radial faces of the cases are to be seen in perspective, end-onview, while the left hand, back end faces are to be thought of assection faces. The insulating cases are in the form of sheet metalhousings full of an insulating filler, as for example rockwool, each ofthe two cases forming a half-shell with a length of about one meter. Thetwo cases may be readily taken off the pipe (after undoing parts joiningthem together which are not to be seen in the figure) and put on thepipe again. The lower case 24 has a pocket 28 stretching in the lengthdirection and normally along the weld in the steam pipe 26, the pocketbeing covered over by a perforated piece of sheet metal 29 (FIG. 5) ifdesired.

In the embodiment of the device of FIG. 4, steam detectors as in FIG. 1or FIG. 2 are used, their pipes 4 running upwards into the pocket 28 sothat, on any steam coming out through a leak, the steam, moving into thepocket 28 for measuring purposes, will take effect on the insulatingmaterial 8 at the top end of pipe 4 (in FIG. 1) or (FIG. 2) will makeits way through the pipe 4 to the insulating material 15. The housings 2of the steam detectors are seated against the lower part of theinsulating case 24. The leads 10 and 11 are connected to a resistanceand/or capacity measuring instrument, which is placed in an instrumentroom, for example in the plant supervisor's office of a nuclear powerplant.

In the device of FIG. 5, a number of steam detectors 18 are placed inthe pocket 28, such detectors being designed as in FIG. 3 or havingelectrodes of some other form within a ceramic body. The steam detectors18 are connected in parallel by wires 30 marked in broken lines.

On steam making its way into pocket 28, it will makes its wayfurthermore into the insulating material of at least one of the steamdetectors so that the ohmic resistance and the capacitance will undergoa sharp drop, at least one of these effects being detected by themeasuring instrument.

If the systems of FIGS. 4 and 5 were made with steam detectors only,false alarms might be produced if, without any steam leaking out of thepipe 26, the insulating material of the steam detectors were to bewetted for some other reason, for example by moisture coming into thepocket 28 from the outside. For stopping false alarms being given insuch cases, there are furthermore temperature feelers or probes whichmay, as in FIGS. 4 and 5, have the form of loops 32. Along each lengthof about one meter it is for example possible to have three spaced loops32, each with a lead 34. Such a design is best if the loops each haveone thermo-element. The thermo-element may then be in the form of a pipethermo-element, the guard pipe forming the one leg of the thermocouple,while a middle wire is the other leg. In place of this, the temperaturefeeler may be in the form of a casing-type thermo-element with the twolegs of the thermocouple insulatingly housed in a metal pipe. As aradiation-resistant material for the thermocouple it is possible to usefor example chromnickel and nickel. By placing such thermo-elements inthe form of generally short loops 32, it is possible to make certainthat any possible leak will never by very far from the sensitive part ofa thermo-element.

In place of the loops 32 as figured, it is possible to have a resistancefeeler, for example in the form of nickel 1000 or platinum 100stretching along the full length of the length of pipe.

When there is a temperature drop, the instruments connected to thefeelers will give a reading because of a drop in voltage at the outputof the thermo-elements while at the output of resistance feelers, theresistance will go down.

The steam detectors and the temperature feelers are connected up by wayof plug contacts on the outside of the insulating cases 24. Eachinsulating material case is then connected to the next cases to it byplug contacts, their leads running to a central instrument room. Suchleads have a high quality insulation and are screened off againstelectro-magnetic fields. The signals from a steam detector on the onehand and from the temperature feelers on the other go for example to theinputs of a warning instrument 35 (FIG. 6) which includes an AND-gate 36and warning device or alarm 37, so that the AND-gate will only give anoutput signal to cause a warning signal from alarm 37 only when thesteam detectors give a signal with respect to the presence of steam ormoisture and similtaneously the temperature feelers give a temperaturedrop signal. It is only in this case that an output signal will beproduced by the instrument, for example for giving an alarm signal orproducing some sort of warning.

It is furthermore to be noted that no output signal will be produced bythe instrument if there is only a drop in temperature in the pocket formeasuring purposes without any leaking of steam. In this case, the steamdetectors will not give any output signal.

I claim:
 1. A device for detecting steam leaking from hollow bodiesabove ground including pipes for gauge pressure steam,comprising:thermal insulation disposed around a said hollow body, therebeing between said insulation and body a space for measuring purposes,temperature change sensor means disposed in said space for providing atleast one output signal response to a predetermined change intemperature in said space, steam detector means having at least inletmeans disposed in said space for providing at least one output signal inthe event steam is sensed by the detector means in said space, saidsteam detector means including at least one steam detector having acapacitor-like structure including a porous insulating material able totake up steam through said inlet means, and warning means connected toreceive said output signals from both the temperature change sensormeans and the steam presence detector means for providing an output onlyupon receiving a said output signal from each simultaneously.
 2. Adevice as claimed in claim 1 wherein:the thermal insulation is dividedinto separate lengths; and said sensor means includes a plurality oftemperature change sensors and said steam detector means includes aplurality of said steam detectors, said sensors and detectors beingpaired at different ones of said lengths, said warning means including aplurality of warning devices respectively coupled to saidsensor-detector pairs for readily determining from which of said lengthsa warning signal is derived.
 3. A device as claimed in claim 2,wherein:the lengths of insulation are divided into at least twosegment-like shells; said space being a longitudinal recess in at leastone of the segment-like shells and being in the form of a channel-likemeasuring pocket running more specially along a weld in said hollowbody; and a plurality of said sensor-detector pairs being disposed alonga length of the pocket.
 4. A device as claimed in claim 3, characterizedin that the signal outputs of the steam detectors of one length areconnected together in parallel.
 5. A device as claimed in claim 3 orclaim 4, characterized in that that signal outputs of the steamdetectors of one length are connected up as such with a respectivewarning device.
 6. A device as claimed in anyone of claims 1, 2, 3 or 4wherein said temperature change sensor means includes resistancefeelers.
 7. A device as claimed in anyone of claims 1, 2, 3 or 4 whereinsaid temperature change sensor means includes thermo-elements.
 8. Adevice as claimed in claim 1, 2, 3 or 4, characterized in that the steamdetector means are located at the outer face of said thermal insulationand have a pipe connected with said space for measuring purposes.
 9. Adevice as claimed in claim 1, 2, 3 or 4, characterized in that the steamdetector means are disposed in a separate pipe which extends throughsaid thermal insulation into said space.
 10. A device as in claim 1, 2,3 or 4 wherein said temperature change sensor means provides an outputsignal only in response to a temperature drop in said space.